Call me unoriginal, but I thought I would copy the title, albeit, mostly, but it is true I cannot get this  working...

typed ./mach build 
into terminal

Then it does this:

0:00.45 /usr/bin/make -f client.mk -s
0:02.46 Adding client.mk options from :
0:02.46 MOZ_OBJDIR=/home/someuser/icedove-uxp/mozilla/obj-x86_64-pc-linux-gnu
0:02.46 OBJDIR=/home/someuser/icedove-uxp/mozilla/obj-x86_64-pc-linux-gnu
0:03.15 cd /home/someuser/icedove-uxp/mozilla/obj-x86_64-pc-linux-gnu
0:03.15 /home/someuser/icedove-uxp/mozilla/configure
0:03.34 Reexecuting in the virtualenv
0:04.08 checking for a shell... /bin/sh
0:04.22 checking for host system type... x86_64-pc-linux-gnu
0:04.22 checking for target system type... x86_64-pc-linux-gnu
0:04.24 checking whether cross compiling... no
0:04.24 checking for pkg_config... /usr/bin/pkg-config
0:04.25 checking for pkg-config version... 0.29.2
0:04.25 checking for yasm... /usr/bin/yasm
0:04.26 checking yasm version... 1.3.0
0:04.28 checking for the target C compiler... /usr/bin/gcc
0:04.34 checking whether the target C compiler can be used... yes
0:04.34 checking the target C compiler version... 8.4.0
0:04.40 checking the target C compiler works... yes
0:04.40 checking for the target C++ compiler... /usr/bin/g++
0:04.45 checking whether the target C++ compiler can be used... yes
0:04.46 checking the target C++ compiler version... 8.4.0
0:04.51 checking the target C++ compiler works... yes
0:04.51 checking for the host C compiler... /usr/bin/gcc
0:04.54 checking whether the host C compiler can be used... yes
0:04.54 checking the host C compiler version... 8.4.0
0:04.60 checking the host C compiler works... yes
0:04.60 checking for the host C++ compiler... /usr/bin/g++
0:04.64 checking whether the host C++ compiler can be used... yes
0:04.64 checking the host C++ compiler version... 8.4.0
0:04.70 checking the host C++ compiler works... yes
0:04.76 checking for 64-bit OS... yes
0:04.83 checking for stdint.h... yes
0:04.89 checking for inttypes.h... yes
0:04.95 checking for malloc.h... yes
0:05.01 checking for alloca.h... yes
0:05.04 checking for sys/byteorder.h... no
0:05.11 checking for getopt.h... yes
0:05.17 checking for unistd.h... yes
0:05.22 checking for nl_types.h... yes
0:05.28 checking for cpuid.h... yes
0:05.34 checking for sys/statvfs.h... yes
0:05.41 checking for sys/statfs.h... yes
0:05.47 checking for sys/vfs.h... yes
0:05.53 checking for sys/mount.h... yes
0:05.60 checking for sys/quota.h... yes
0:05.68 checking for linux/quota.h... yes
0:05.76 checking for linux/if_addr.h... yes
0:05.86 checking for linux/rtnetlink.h... yes
0:05.91 checking for sys/queue.h... yes
0:05.98 checking for sys/types.h... yes
0:06.05 checking for netinet/in.h... yes
0:06.11 checking for byteswap.h... yes
0:06.18 checking for linux/perf_event.h... yes
0:06.23 checking for perf_event_open system call... yes
0:06.25 checking whether the C compiler supports -Wclass-varargs... no
0:06.27 checking whether the C++ compiler supports -Wclass-varargs... no
0:06.30 checking whether the C compiler supports -Wloop-analysis... no
0:06.32 checking whether the C++ compiler supports -Wloop-analysis... no
0:06.36 checking whether the C++ compiler supports -Wc++11-compat-pedantic... no
0:06.40 checking whether the C++ compiler supports -Wc++14-compat... yes
0:06.44 checking whether the C++ compiler supports -Wc++14-compat-pedantic... no
0:06.49 checking whether the C++ compiler supports -Wc++1z-compat... yes
0:06.55 checking whether the C++ compiler supports -Wimplicit-fallthrough... yes
0:06.57 checking whether the C compiler supports -Wstring-conversion... no
0:06.60 checking whether the C++ compiler supports -Wstring-conversion... no
0:06.62 checking whether the C compiler supports -Wthread-safety... no
0:06.64 checking whether the C++ compiler supports -Wthread-safety... no
0:06.68 checking whether the C++ compiler supports -Wno-inline-new-delete... no
0:06.73 checking whether the C compiler supports -Wno-error=maybe-uninitialized... yes
0:06.79 checking whether the C++ compiler supports -Wno-error=maybe-uninitialized... yes
0:06.84 checking whether the C compiler supports -Wno-error=deprecated-declarations... yes
0:06.90 checking whether the C++ compiler supports -Wno-error=deprecated-declarations... yes
0:06.94 checking whether the C compiler supports -Wno-error=array-bounds... yes
0:07.00 checking whether the C++ compiler supports -Wno-error=array-bounds... yes
0:07.04 checking whether the C compiler supports -Wno-error=multistatement-macros... yes
0:07.09 checking whether the C++ compiler supports -Wno-error=multistatement-macros... yes
0:07.15 checking whether the C++ compiler supports -Wno-noexcept-type... yes
0:07.16 checking for awk... /usr/bin/gawk
0:07.16 checking for perl... /usr/bin/perl
0:07.17 checking for minimum required perl version >= 5.006... 5.030003
0:07.19 checking for full perl installation... yes
0:07.19 checking for gmake... /usr/bin/make
0:07.19 checking for doxygen... /usr/bin/doxygen
0:07.19 checking for xargs... /usr/bin/xargs
0:07.20 checking for rpmbuild... not found
0:07.20 checking for autoconf... /usr/bin/autoconf-2.13
0:07.30 loading cache ./config.cache
0:07.36 checking host system type... x86_64-pc-linux-gnu
0:07.39 checking target system type... x86_64-pc-linux-gnu
0:07.43 checking build system type... x86_64-pc-linux-gnu
0:07.44 checking for gcc... (cached) /usr/bin/gcc -std=gnu99
0:07.52 checking whether the C compiler (/usr/bin/gcc -std=gnu99 ) works... yes
0:07.52 checking whether the C compiler (/usr/bin/gcc -std=gnu99 ) is a cross-compiler... no
0:07.52 checking whether we are using GNU C... (cached) yes
0:07.52 checking whether /usr/bin/gcc -std=gnu99 accepts -g... (cached) yes
0:07.52 checking for c++... (cached) /usr/bin/g++ -std=gnu++11
0:07.73 checking whether the C++ compiler (/usr/bin/g++ -std=gnu++11 ) works... yes
0:07.73 checking whether the C++ compiler (/usr/bin/g++ -std=gnu++11 ) is a cross-compiler... no
0:07.73 checking whether we are using GNU C++... (cached) yes
0:07.73 checking whether /usr/bin/g++ -std=gnu++11 accepts -g... (cached) yes
0:07.73 checking for ranlib... (cached) ranlib
0:07.73 checking for as... (cached) /usr/bin/as
0:07.73 checking for ar... (cached) ar
0:07.73 checking for ld... (cached) ld
0:07.73 checking for strip... (cached) strip
0:07.73 checking for windres... no
0:07.78 checking for sb-conf... no
0:07.78 checking for ve... no
0:07.79 checking for X... (cached) libraries /usr/lib64, headers
0:07.80 checking for dnet_ntoa in -ldnet... (cached) no
0:07.81 checking for dnet_ntoa in -ldnet_stub... (cached) no
0:07.81 checking for gethostbyname... (cached) yes
0:07.81 checking for connect... (cached) yes
0:07.81 checking for remove... (cached) yes
0:07.82 checking for shmat... (cached) yes
0:07.83 checking for IceConnectionNumber in -lICE... (cached) yes
0:08.61 checking for --noexecstack option to as... yes
0:08.72 checking for -z noexecstack option to ld... yes
0:08.82 checking for -z text option to ld... yes
0:08.91 checking for --build-id option to ld... yes
0:09.01 checking for working const... (cached) yes
0:09.01 checking for mode_t... (cached) yes
0:09.01 checking for off_t... (cached) yes
0:09.01 checking for pid_t... (cached) yes
0:09.01 checking for size_t... (cached) yes
0:09.02 checking for ssize_t... (cached) yes
0:09.02 checking whether 64-bits std::atomic requires -latomic... (cached) no
0:09.02 checking for dirent.h that defines DIR... (cached) yes
0:09.04 checking for opendir in -ldir... (cached) no
0:09.04 checking for gethostbyname_r in -lc_r... (cached) no
0:09.04 checking for library containing dlopen... (cached) -ldl
0:09.05 checking for dlfcn.h... (cached) yes
0:09.06 checking for socket in -lsocket... (cached) no
0:09.07 checking for pthread_create in -lpthreads... (cached) no
0:09.07 checking for pthread_create in -lpthread... (cached) yes
0:09.17 checking whether /usr/bin/gcc -std=gnu99 accepts -pthread... yes
0:09.17 checking whether /usr/bin/gcc -std=gnu99 needs -traditional... (cached) no
0:09.17 checking for 8-bit clean memcmp... (cached) yes
0:09.18 checking for getc_unlocked... (cached) yes
0:09.19 checking for _getc_nolock... (cached) no
0:09.19 checking for gmtime_r... (cached) yes
0:09.20 checking for localtime_r... (cached) yes
0:09.21 checking for pthread_getname_np... (cached) yes
0:09.21 checking for clock_gettime(CLOCK_MONOTONIC)... (cached)
0:09.23 checking for sin in -lm... (cached) yes
0:09.24 checking for sincos in -lm... (cached) yes
0:09.25 checking for __sincos in -lm... (cached) no
0:09.25 checking for wcrtomb... (cached) yes
0:09.25 checking for mbrtowc... (cached) yes
0:09.26 checking for res_ninit()... (cached) yes
0:09.26 checking for nl_langinfo and CODESET... (cached) yes
0:09.27 checking for an implementation of va_copy()... (cached) yes
0:09.27 checking whether va_list can be copied by value... (cached) no
0:09.28 checking whether the C++ "using" keyword resolves ambiguity... (cached) yes
0:09.29 checking for C++ dynamic_cast to void... (cached) yes
0:09.29 checking for thread keyword for TLS variables... (cached) yes
0:09.30 checking for __attribute((always_inline))... (cached) yes
0:09.30 checking for LC_MESSAGES... (cached) yes
0:09.31 checking for localeconv... (cached) yes
0:09.32 checking NSPR selection... posix-wrapper
0:09.33 checking for gzread in -lz... (cached) yes
0:09.48 checking for valid optimization flags... yes
0:09.50 checking for __cxa_demangle... (cached) yes
0:09.58 checking whether C compiler supports -fprofile-generate... yes
0:09.58 checking for tm_zone tm_gmtoff in struct tm... (cached) yes
0:09.70 checking what kind of list files are supported by the linker... linkerscript
0:09.79 checking what kind of ordering can be done with the linker... section-ordering-file
0:09.81 checking for posix_fadvise... (cached) yes
0:09.82 checking for posix_fallocate... (cached) yes
0:09.84 checking for malloc.h... (cached) yes
0:09.84 checking for strndup... (cached) yes
0:09.86 checking for posix_memalign... (cached) yes
0:09.86 checking for memalign... (cached) yes
0:09.88 checking for malloc_usable_size... (cached) yes
0:09.92 checking whether malloc_usable_size definition can use const argument... no
0:09.95 checking for valloc in malloc.h... yes
0:09.97 checking for valloc in unistd.h... no
0:09.98 checking for setlocale... (cached) yes
0:09.99 checking for localeconv... (cached) yes
0:10.02 creating ./config.data
0:10.22 Creating config.status
0:10.36 Walking the dog...
0:10.90 Traceback (most recent call last):
0:10.90 File "/home/someuser/icedove-uxp/mozilla/configure.py", line 107, in <module>
0:10.90 sys.exit(main(sys.argv))
0:10.90 File "/home/someuser/icedove-uxp/mozilla/configure.py", line 31, in main
0:10.90 return config_status(config)
0:10.90 File "/home/someuser/icedove-uxp/mozilla/configure.py", line 102, in config_status
0:10.90 return config_status(args=[], *encode(sanitized_config, encoding))
0:10.90 File "/home/someuser/icedove-uxp/mozilla/python/mozbuild/mozbuild/config_status.py", line 135, in config_status
0:10.90 definitions = list(definitions)
0:10.90 File "/home/someuser/icedove-uxp/mozilla/python/mozbuild/mozbuild/frontend/emitter.py", line 185, in emit
0:10.90 objs = list(self._emit_libs_derived(contexts))
0:10.90 File "/home/someuser/icedove-uxp/mozilla/python/mozbuild/mozbuild/frontend/emitter.py", line 219, in _emit_libs_derived
0:10.90 self._link_libraries(context, obj, variable)
0:10.90 File "/home/someuser/icedove-uxp/mozilla/python/mozbuild/mozbuild/frontend/emitter.py", line 332, in _link_libraries
0:10.90 context)
0:10.90 mozbuild.frontend.reader.SandboxValidationError:
0:10.90 ==============================
0:10.90 ERROR PROCESSING MOZBUILD FILE
0:10.90 ==============================
0:10.90
0:10.90 The error occurred while processing the following file or one of the files it includes:
0:10.90
0:10.90 /home/someuser/icedove-uxp/mozilla/js/src/moz.build
0:10.90
0:10.90 The error occurred when validating the result of the execution. The reported error is:
0:10.90
0:10.90 USE_LIBS contains "icu", which does not match any LIBRARY_NAME in the tree.
0:10.90
0:10.90
0:10.97 Fix above errors and then restart with\
0:10.97 "/usr/bin/make -f client.mk build"
0:10.97 make[2]: [/home/someuser/icedove-uxp/mozilla/client.mk:377: configure] Error 1
0:10.97 make[1]: [/home/someuser/icedove-uxp/mozilla/client.mk:390: /home/someuser/icedove-uxp/mozilla/obj-x86_64-pc-linux-gnu/Makefile] Error 2
0:10.97 make: [client.mk:169: build] Error 2
0:10.98 0 compiler warnings present.

and then it stops...

Not sure what I need to do. Also, it could have the errors that iceweasel has too, so I better wait for more instructions.

Btw, tch, if you could help, it would be greatly appreciated.

not really on topic, but still not sure what a bucket of footsmell is.

But yeah,  I am stumped. I tried disabling icu, although maybe I am missing something as to why I can't...

Idk. lol

EDIT: I meant to say 2.6 as 3.1 doesn't exist for icedove-uxp LOL!